scholarly journals Another relic bulge globular cluster: ESO 456-SC38 (Djorgovski 2)

2019 ◽  
Vol 627 ◽  
pp. A145 ◽  
Author(s):  
S. Ortolani ◽  
E. V. Held ◽  
D. Nardiello ◽  
S. O. Souza ◽  
B. Barbuy ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Milky Way ◽  
Galactic Center ◽  
Horizontal Branch ◽  
Very Old ◽  
Orbital Parameters ◽  
Data Release ◽  
Best Fitting ◽  
Bulge Formation

Context. The object ESO 456-SC38 (Djorgovski 2) is one of the globular clusters that is closest to the Galactic center. It is on the blue horizontal branch and has a moderate metallicity of [Fe/H] ∼ −1.0. It is thus similar to the very old inner bulge globular clusters NGC 6522, NGC 6558, and HP 1, and therefore appears to be part of the primeval formation stages of the Milky Way. Aims. The aim of this work is to determine an accurate distance and metallicity for ESO 456-SC38, as well as orbital parameters, in order to check similarities with other clusters in the inner bulge that have previously been well studied in terms of spectroscopy and photometry. This is a considerably fainter cluster that is contaminated by a rich stellar field; it is also quite absorbed by the dusty foreground. Methods. We analyzed ESO 456-SC38 based on HST photometry, with the filters F606W from ACS, F110W and F160W from WFC3, and photometry in V and I from FORS2 at the VLT. We combined this with identified stars that are covered by Gaia Data Release 2. Results. The isochrone fitting was carried out with the statistical Markov chain Monte Carlo method. We derive an accurate distance of d⊙ = 8.75 ± 0.12 kpc and a reddening of E(B−V) = 0.81+0.02−0.02. The best-fitting BaSTI isochrones correspond to an age of 12.70+0.72−0.69 Gyr and a metallicity of [Fe/H] = −1.11+0.03−0.03. Conclusions. ESO 456-SC38 adds to the list of moderately metal-poor globular clusters located in the inner bulge. It has a blue horizontal branch and is very old. The cluster is confined to the bulge and bar region, but it does not support the Galactic bar structure. The old stellar population represented by clusters like this has to be taken into account in models of Galactic bulge formation. Studying them also provides indications on the formation times of the globular clusters themselves.

scholarly journals Gaia Data Release 2

2018 ◽  
Vol 616 ◽  
pp. A12 ◽  
Author(s):  
◽  
A. Helmi ◽  
F. van Leeuwen ◽  
P. J. McMillan ◽  
D. Massari ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Proper Motions ◽  
Single Plane ◽  
Dwarf Spheroidal Galaxies ◽  
Orbital Parameters ◽  
Data Release ◽  
Using Data

Context. Aims. The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds. Methods. Using data extracted from the Gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community. Results. Our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (iv) derive a lower limit for the mass of the Milky Way of 9.1-2.6+6.2 × 1011 M⊙ based on the assumption that the Leo I dwarf spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (vi) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud. Conclusions. All these results highlight the incredible power of the Gaia astrometric mission, and in particular of its second data release.

scholarly journals Stellar parameters in the bulge cluster NGC 6553

1997 ◽  
Vol 189 ◽  
pp. 203-206 ◽  
Author(s):  
B. Barbuy ◽  
S. Ortolani ◽  
E. Bica ◽  
A. Renzini ◽  
M.D. Guarnieri
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Spectroscopic Analysis ◽  
Galactic Center ◽  
Stellar Populations ◽  
The Sun ◽  
Galactic Bulge ◽  
Complete Understanding ◽  
Luminosity Functions ◽  
Bulge Formation

Globular clusters in the Galactic bulge form a flattened system, extending from the Galactic center to about 4.5 kpc from the Sun (Barbuy et al. 1997). A study of abundance ratios in these clusters is very important for a more complete understanding of the bulge formation. In this work we present a spectroscopic analysis of individual stars in NGC 6553. This cluster is a key one because it is located at d⊙ ≍ 5.1 kpc, therefore relatively close to us, and at the same time it is representative of the Galactic bulge stellar population: (a) Ortolani et al. (1995) showed that NGC 6553 and NGC 6528 show very similar Colour-Magnitude Diagrams (CMDs), and NGC 6528 is located at d⊙ ≍ 7.83 kpc, very close to the Galactic center; (b) the stellar populations of the Baade Window is also very similar to that of NGC 6553 and NGC 6528 as Ortolani et al. (1995) have shown by comparing their luminosity functions.

scholarly journals The eye of Gaia on globular clusters structure: tidal tails

2020 ◽  
Vol 495 (2) ◽  
pp. 2222-2233 ◽  
Author(s):  
A Sollima
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Milky Way ◽  
Field Of View ◽  
Proper Motions ◽  
Mixture Modelling ◽  
Background Density ◽  
Data Release ◽  
Observational Estimate ◽  
Tidal Tails

ABSTRACT I analyse the projected density distribution of member stars over a wide area surrounding 18 Galactic globular clusters using the photometric and astrometric information provided by the second data release of the Gaia mission. A 5D mixture modelling technique has been employed to optimally isolate the signal of the cluster stellar population from the contamination of the Galactic field, taking advantage of its different distribution in the space formed by colours, magnitudes, parallaxes, and proper motions. In 7 clusters I detect collimated overdensities at a >3σ level above the background density extending well beyond the cluster tidal radius, consistent with the distortion expected as a result of the tidal interaction with the Milky Way potential. In five of these clusters (NGC 288, NGC 2298, NGC 5139, NGC 6341, and NGC 7099) spectacular tidal tails extend up to the border of the analysed field of view at 5 deg from the centre. At large distances from the cluster centre, the orientation of the detected overdensities appears to be systematically aligned with the cluster orbital path, in agreement with the predictions of N-body simulations. The fraction of stars contained in the tidal tails of these clusters is also used to determine the first observational estimate of their present-day destruction rates.

scholarly journals 1.9. Globular clusters within 5° of the Galactic center

1998 ◽  
Vol 184 ◽  
pp. 33-34
Author(s):  
B. Barbuy ◽  
E. Bica ◽  
S. Ortolani
Keyword(s):  
Spatial Distribution ◽  
Globular Clusters ◽  
Stellar Population ◽  
Galactic Center ◽  
Observational Constraints ◽  
Galactic Bulge ◽  
Very Old

The knowledge of age and spatial distribution of stars in the Galactic bulge require observational constraints to establish whether its stellar population is very old (Larson 1990) or is a younger, disk-like component (Raha et al. 1992), and if its shape is spherical or extended, or perhaps a bar (Blitz & Spergel 1991). Yet other possibilities are a flattened bulge or a disk-like system (Zinn 1985; Armandroff 1989; Ortolani et al. 1993; Minniti 1995).

scholarly journals The WAGGS project-III. Discrepant mass-to-light ratios of Galactic globular clusters at high metallicity

2020 ◽  
Vol 492 (3) ◽  
pp. 3859-3871 ◽  
Author(s):  
H Dalgleish ◽  
S Kamann ◽  
C Usher ◽  
H Baumgardt ◽  
N Bastian ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Milky Way ◽  
Population Models ◽  
Theoretical Predictions ◽  
Field Unit ◽  
Stellar Masses ◽  
Kinematic Information ◽  
High Metallicity ◽  
Integral Field

ABSTRACT Observed mass-to-light ratios (M/L) of metal-rich globular clusters (GCs) disagree with theoretical predictions. This discrepancy is of fundamental importance since stellar population models provide the stellar masses that underpin most of extragalactic astronomy, near and far. We have derived radial velocities for 1622 stars located in the centres of 59 Milky Way GCs – 12 of which have no previous kinematic information – using integral-field unit data from the WAGGS project. Using N-body models, we determine dynamical masses and M/LV for the studied clusters. Our sample includes NGC 6528 and NGC 6553, which extend the metallicity range of GCs with measured M/L up to [Fe/H] ∼ −0.1 dex. We find that metal-rich clusters have M/LV more than two times lower than what is predicted by simple stellar population models. This confirms that the discrepant M/L–[Fe/H] relation remains a serious concern. We explore how our findings relate to previous observations, and the potential causes for the divergence, which we conclude is most likely due to dynamical effects.

scholarly journals An Overview of the Globular Cluster System of the Galaxy

1988 ◽  
Vol 126 ◽  
pp. 37-48
Author(s):  
Robert Zinn
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Cluster System ◽  
Open Clusters ◽  
The Galaxy ◽  
Globular Cluster System ◽  
Harlow Shapley

Harlow Shapley (1918) used the positions of globular clusters in space to determine the dimensions of our Galaxy. His conclusion that the Sun does not lie near the center of the Galaxy is widely recognized as one of the most important astronomical discoveries of this century. Nearly as important, but much less publicized, was his realization that, unlike stars, open clusters, HII regions and planetary nebulae, globular clusters are not concentrated near the plane of the Milky Way. His data showed that the globular clusters are distributed over very large distances from the galactic plane and the galactic center. Ever since this discovery that the Galaxy has a vast halo containing globular clusters, it has been clear that these clusters are key objects for probing the evolution of the Galaxy. Later work, which showed that globular clusters are very old and, on average, very metal poor, underscored their importance. In the spirit of this research, which started with Shapley's, this review discusses the characteristics of the globular cluster system that have the most bearing on the evolution of the Galaxy.

scholarly journals Did the Bulge Form All at Once?

1996 ◽  
Vol 169 ◽  
pp. 403-410
Author(s):  
R.M. Rich
Keyword(s):  
Galaxy Evolution ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Center ◽  
Field Population ◽  
Dynamical Instability ◽  
Galactic Bulge ◽  
Recent Developments ◽  
Order Of Magnitude ◽  
History Of

It is reasonable to say that if Jan Oort were alive today, he would no doubt find recent developments in the study of the Galactic bulge to be fascinating. Oort considered the Galactic bulge in two contexts. First, he was interested in the use of the RR Lyrae stars as probes to determine the distance to the Galactic Center. No doubt, Oort would have been excited about the growing evidence of the bulge's triaxiality, as well as by the debate over the age of the bulge. His second interest was in the nature of activity at the center, an issue that I will not discuss in this review. The latter also remains an unsolved problem of the Milky Way, and (based on his work) one that might have been nearer to his heart than this one. Yet the question of when the bulge formed is ultimately a question about the formation history of the Galaxy. The oldest stars (those whose ages we are certain of) are found in Galactic globular clusters, the sum total of which are ≈ 5 × 107M⊙. The field population of the bulge is ≈ 2–3 × 1010M⊙, an order of magnitude more massive than the field population of the metal poor spheroid. So if the bulge formed all at once, and early, then the Milky Way had a luminous, even cataclysmic youth. But if the bulge formed later in the history of our galaxy, as a starburst or dynamical instability of the central disk, then the young Milky Way may have been inconspicuous and primeval galaxies may be hard to find indeed. If our bulge formed very early, its stellar population might have much in common with the giant ellipticals, while a late bulge might teach us much about processes that affect galaxy evolution.

scholarly journals Was the Milky Way Bulge Formed from the Buckling Disk Instability, Hierarchical Collapse, Accretion of Clumps, or All of the Above?

2017 ◽  
Vol 34 ◽  
Author(s):  
David M. Nataf
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Velocity Dispersion ◽  
High Redshift ◽  
Rapid Development ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
Thin And Thick Disks ◽  
Bulge Formation ◽  
Redshift Galaxies

AbstractThe assembly of the Milky Way bulge is an old topic in astronomy, one now in a period of renewed and rapid development. That is due to tremendous advances in observations of bulge stars, motivating observations of both local and high-redshift galaxies, and increasingly sophisticated simulations. The dominant scenario for bulge formation is that of the Milky Way as a nearly pure disk galaxy, with the inner disk having formed a bar and buckled. This can potentially explain virtually all bulge stars with [Fe/H] ≳ −1.0, which comprise 95% of the stellar population. The evidence is the incredible success in N-body models of this type in making non-trivial, non-generic predictions, such as the rotation curve and velocity dispersion measured from radial velocities, and the spatial morphologies of the peanut/X-shape and the long bar. The classical bulge scenario, whereby the bulge formed from early dissipative collapse and mergers, remains viable for stars with [Fe/H] ≲ −1.0 and potentially a minority of the other stars. A classical bulge is expected from Λ-CDM cosmological simulations, can accentuate the properties of an existing bar in a hybrid system, and is most consistent with the bulge abundance trends such as [Mg/Fe], which are elevated relative to both the thin and thick disks. Finally, the clumpy-galaxy scenario is considered, as it is the correct description of most Milky Way precursors given observations of high-redshift galaxies. Simulations predict that these star-forming clumps will sometimes migrate to the centres of galaxies where they may form a bulge, and galaxies often include a bulge clump as well. They will possibly form a bar with properties consistent with those of the Milky Way, such as the exponential profile and metallicity gradient. Given the relative successes of these scenarios, the Milky Way bulge is plausibly of composite origin, with a classical bulge and/or inner halo numerically dominant for stars with [Fe/H] ≲ −1.0, a buckling thick disk for stars with − 1.0 ≲ [Fe/H]] ≲ -0.50 perhaps descended from the clumpy-galaxy phase, and a buckling thin disk for stars with [Fe/H] ≳ −0.50. Overlaps from these scenarios are uncertain throughout.

scholarly journals Population Models for Massive Globular Clusters

2012 ◽  
Vol 10 (H16) ◽  
pp. 247-248 ◽  
Author(s):  
Young-Wook Lee ◽  
Seok-Joo Joo ◽  
Sang-Il Han ◽  
Chongsam Na ◽  
Dongwook Lim ◽  
...  
Keyword(s):  
Parameter Space ◽  
Globular Clusters ◽  
Heavy Element ◽  
Milky Way ◽  
Population Modeling ◽  
Stellar Populations ◽  
Population Models ◽  
Horizontal Branch ◽  
Element Abundances ◽  
Hr Diagram

Increasing number of massive globular clusters (GCs) in the Milky Way are now turned out to host multiple stellar populations having different heavy element abundances enriched by supernovae. Recent observations have further shown that [CNO/Fe] is also enhanced in metal-rich subpopulations in most of these GCs, including ω Cen and M22 (Marino et al. 2011, 2012). In order to reflect this in our population modeling, we have expanded the parameter space of Y2 isochrones and horizontal-branch (HB) evolutionary tracks to include the cases of normal and enhanced nitrogen abundances ([N/Fe] = 0.0, 0.8, and 1.6). The observed variations in the total CNO content were reproduced by interpolating these nitrogen enhanced stellar models. Our test simulations with varying N and O abundances show that, once the total CNO sum ([CNO/Fe]) is held constant, both N and O have almost identical effects on the HR diagram (see Fig. 1).

scholarly journals CN Anomalies in the Halo System

2012 ◽  
Vol 10 (H16) ◽  
pp. 282-283
Author(s):  
Daniela Carollo
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Strong Field ◽  
Significant Source ◽  
Red Giants ◽  
Orbital Parameters ◽  
Halo Stars ◽  
Halo Population ◽  
Absorption Features ◽  
Kinematic Properties

AbstractI present an evaluation of the kinematic properties of halo red giants thought to have formed in globular clusters based on the strength of their UV/blue CN and CH absorption features. The sample has been selected from the catalog of Martell et al. (2011). The orbital parameters of CN-strong halo stars are compared to those of the inner and outer halo populations, and to the orbital parameters of globular clusters with well-studied Galactic orbits. It has been found that both the clusters and the CN-strong field stars exhibit kinematic and orbital properties similar to the inner halo population, indicating that globular clusters could be a significant source of inner halo field stars, and suggesting that both globular clusters and CN-strong stars could belong primarily to the inner halo population of the Milky Way.

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